..PDM-BPSK allowed transmission distances in excess of 14,040 km to be achieved, compared to 13,640 km for PS-QPSK. However, PS-QPSK offers a significant reduction in receiver complexity due to the lower symbol-rate...

Generation and long-haul transmission of polarization-switched QPSK at 42.9 Gb/s

David S MillarOptical Networks Group, Department of Electronic and Electrical Engineering, University College London UCL, Torrington Place, London WC1E 7JE, United KingdomOpt Express 19:9296-302. 2011

..The maximum reach of 13640 km for WDM PS-QPSK is, to the best of our knowledge, the longest distance reported for 40 Gb/s WDM transmission, over an uncompensated link, with standard fiber and amplification...